Piston ring and process of making the same

ABSTRACT

A cast iron piston ring is provided with a friction reducing packing of bonded iron oxide nd carbon powder in a groove of its outer circumferential face, and with a hard chromium electrodeposit on all other surfaces by first applying a packing composition including a heat curing bonding agent, thereafter coating the packing with an aqueous polytetrafluoroethylene dispersion, drying and sintering the resin into a continuous film while simultaneously curing the packing, and thereafter electrodepositing chromium, the cured packing being protected against attack by the chromium plating bath by the resin film.

United States Patent Umezawa 1 June 20, 1972 [54] PISTON RING ANDPROCESS ()F 2,614,899 10/1952 Phillips ..277/235 A MAKING THE SAL/[E3,467,397 9/1969 Sugahara ..277/ 139 3,615,099 10/1971 Prasse ..277/235A [72] Inventor: Koujl Umezawa, Konosu, Japan Primary Examiner-Robert l.Smith [73] Assignee. Nippon Piston Ring Kabushiki Kaisha, An0mey Kelmanand Barman Toyko, Japan [22] Filed: Nov. 10, 1970 211 Appl. No.: 88,320[57] ABSIRACT A cast iron piston ring is provided with a frictionreducing packing of bonded iron oxide nd carbon powder in a groove of[30] Fnrdgn Application Priority Data its outer circumferential face,and with a hard chromium elec- Nov. 18, 1969 Japan ..44/92388 trodepositon all other surfaces by first applying a packing composition includinga heat curing bonding agent, thereafter [52] US. Cl. ..277/235 R, 29/156.63 coating the packing with an aqueous polytetrafluoroethylene [51]lnl.Cl ..Fl6j 9/12 dispersion, drying and sintering the resin into acontinuous [58] Field of Search ..29/ 156.63; 277/235 R, 235 A, filmwhile simultaneously curing the packing, and thereafter 277/D1G. 6, 138,139, 140; 117/71 M electrodepositing chromium, the cured packing beingprotected against attack by the chromium plating bath by the [56]References Cited resin film.

UNITED STATES PATENTS 4 Claims, 1 Drawing Figure Anderson 277/l38 PISTONRING AND PROCEQS OF MAKING THESAME This invention relates to pistonrings suitable for automotive internal-combustion engines and to aprocess of making such piston rings.

In its more specific aspects, this invention relates to a piston ringcarrying an antifriction packing of bonded iron'oxide (Fe O,) and carbonpowder mixture in a groove of the outer circumferential ring face.

Piston rings provided with such a packing have been-found useful inreducing friction in a seal between the piston and the cooperatingcylinder at high compression ratios, and to retain their effectivenessafter extended service at high piston speeds. The known packings containwaterglass (aqueous sodium silicate) or a thermosetting resincomposition as a bonding agent, and require heat treatment at elevatedtempcrature for curing the bonding agent.

- It is also known to provide piston rings with chromium electrodepositsfor low friction and wear resistance, and it is common good practice todeposit chromium at a Vickers Pyramid Hardness of more than700,-preferably 850 to 1,000. However, it has not been possibleheretofore to make a piston ring having both an outer circumferentialpacking of baked iron oxide and carbon while being covered with hardelectrodeposited chromium on all or any other surface.

If the piston ring is chromium plated before receiving the ironoxide-carbon powder mixture, the hardness of the elec trodeposit isreduced to about 650 VPl-l in the heat treatment. If the powder isapplied and baked prior to electrodeposition, the chromium platingsolution corrodes the antifriction material and makes it unsuited forthe intended purpose.

it is an object of this invention to provide a piston ring whichcombines the advantages of a bonded packing of the type described withthose of a hard chromium coating on at least one surface other than theouter circumferential surface of the piston ring. a

Another object is the provision of a process of making such a pistonring.

It has now been found that the powder mixture may be coated prior toheat treatment with a fluoroplastic resin composition perature for thepowder mixture, of withstanding attack by the chromium plating bath, andof protecting the packing, and that the heat treated piston ring maythereafter be subjected to chromium plating without attack on the curedpacking. The thin film of resin is an effective lubricant under thenormal conditions of piston ring use for at least the breaking-inperiod, and does not interfere with the operation of the cured packing,nor shorten its useful life.

Other features and many of the attendant advantages of this inventionwill readily be appreciated as the same becomes better understood byreference to the following detailed description of a preferredembodiment when considered in connection with the appended drawing.

The sole FIGURE of the drawing shows a piston ring prepared by theprocess of the invention in fragmentary section on its axis.

The body 1 of the ring consists of cast iron. It is of generallyrectangular cross section, the relatively narrow, outer, circumferentialface 2 of the piston ring body being formed with a shallow annulargroove 3 extending over much of the axial.

height of the ring.

The groove 3 is filled with a packing 4 of bonded iron oxide and carbonpowder. The wide upper and lower radial faces 5, 6 of the piston ringbody 1, and the inner, circumferential face 7 are covered with a coating8 of electrodeposited chromium. A film 9 of polytetrafluoroethylene(TFE) covers the exposed face of the packing 4.

in an actual embodiment of theinvention, the piston ring body 1 had anouter diameter of 83 mm, an axial height of 1.9

mm, and a radial width of 3.4 mm. The groove 3 and the.

packing conformingly received therein had cross-sectional dimensions of0.5 mm in the direction of the ring diameter,

and 0.45 mm in the direction of the piston ring axis. The

chromium electrodeposit 8 had a thickness of 8 microns, while capable ofbeing heated-to an adequate curing temthe polytetrafluoroethylene filmhad a thickness of 55 microns in the finished piston ring.

In producing the ring, the groove 3 was packed with the conventionalmixture of iron oxide, carbon, and waterglass bonding agent. A layer ofTFE powder dispersion containing a small amount of temporary binder inits aqueous medium was applied over the exposed portion of thecircumferential ring face 2 and the exposed face of the green packing 4,and the ring was thereafter slowly heated to evaporate the waterpresent, at about 200 C. in l hour, and thereafter simultaneously tocure the TFB layer which coalesced into a gel, and the powder mixture.The ultimate temperature was somewhat below 390 C, but above thesintering temperature for the TFE composition. The coated piston ringwas then cooled slowly to solidify the TFE layer into a continuous film.

lt was next immersed in a chromium plating bathand made the cathode inthe bath untilchromium was deposited to the average thickness indicatedabove. The bath, conventional in itself, contained 250 g/l chromiumtrioxide, approximately l.4 g/l sulfuric acid, and 5.5 g/l sodiumfluosilicate. lts temperature was 65i2 C, andthe cathode current densitywas controlled at 60 to amps./dm

Careful examination of a cross section showed that none of the chromiumplating solution had penetrated into the packing, and thus could notcause oxidation of the mo, and the resulting loss of coherence whichcould cause the packing to be dislodged during service.

The piston ring prepared as described performed well in extended serviceunder taxing conditions.

While TFE is preferred at this time as a material for the fluoroplasticfilm 9, the several other fluoroplastics now in commercial use,including polychlorotrifluoroethylene, fiuorinated ethylene propylenepolymer, or polyvinylidene fluoride may be substituted with thenecessary changes in processing conditions, particularlyin the sinteringtemperature.

The thickness of the fluoroplastic film 9 may be chosen to suitrequirements, that is, adequately to protect the cured powder mixture,and the optimum value depends on variables relating both to the pistonring and to the cylinder in which the piston ring is to be used. Someexperimentation thus is unavoidable, but a thickness of approximately 50microns or. more in the cured fluoroplastic and a correspondingthickness of the applied dispersion will normally give good results.Similar considerations hold for the chromium electrodeposit, and thoseskilled in the art will modify the procedure outlined above to meetspecific requirements. A chromium layer less than 5 microns thick israrely adequate. The metal employed for the body portion of the ring mayrequire changes in the chromium thickness in an obvious manner.

It should be understood, therefore, that many modifications andvariations of the present invention are possible in the light of theabove teachings, and that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically described.

What is claimed is:

l. A piston ring comprising, in combination:

a. an annular, metallic body portion formed with a groove in the outercircumferential face thereof;

b; a packing of mixed, bonded iron oxide powder and carbon powderfilling said groove;

c. a film of fluoroplastic resin composition covering the ex- 7 posedface of said packing; and

d. an electrodeposit of chromium on at least one other face of said bodyportion, said electrodeposit having a Vickers Pyramid Hardness greaterthan 700.

2. A piston ring as set forth in claim 1, wherein the thickness of saidfilm'is not substantially smaller than 50 microns, nor the thickness ofsaid electrodeposit substantially smaller than 5 microns on an average.

3. A piston ring as set forth in claim 2, said fluoroplastic resincomposition being polytetrafluoroethylene, polychlorotrifluoroethylene,fluorinated ethylene propylene polymer, or polyvinylidene fluoride.

4. A piston ring as set forth in claim 2, said fluoroplastic resincomposition being polytetrafluoroethylene.

2. A piston ring as set forth in claim 1, wherein the thickness of saidfilm is not substantially smaller than 50 microns, nor the thickness ofsaid electrodeposit substantially smaller than 5 microns on an average.3. A piston ring as set forth in claim 2, said fluoroplastic resincomposition being polytetrafluoroethylene, polychlorotrifluoroethylene,fluorinated ethylene propylene polymer, or polyvinylidene fluoride.
 4. Apiston ring as set forth in claim 2, said fluoroplastic resincomposition being polytetrafluoroethylene.